Phenol and methyl ethyl ketone are important products in the chemical industry. For example, phenol is useful in the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, alkyl phenols, and plasticizers, whereas methyl ethyl ketone can be used as a lacquer, a solvent and for dewaxing of lubricating oils.
The most common route for the production of methyl ethyl ketone is by dehydrogenation of sec-butyl alcohol (SBA), with the alcohol being produced by the acid-catalyzed hydration of butenes. Commercial scale SBA manufacture by butylene with sulfuric acid has be accomplished for many years via gas/liquid extraction. Improvements to this hydration process include a process configuration that utilizes a unique combination of plug flow, bubble column, and CSTR (Stirred Tank Reactor) reaction sections to achieve high conversion of butylene. Other improved processes use spargers, custom-designed for butylene/sulfuric acid absorption/extraction. Also, loop reactors may be preferred to improve mixing intensity. In sec-butyl alcohol dehydrogenation, crude sec-butyl alcohol is recovered in absorption or extraction sections using several towers, preferably, a single tower, to separate sec-butyl alcohol from sec-butyl ether.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. However, the world demand for phenol is growing more rapidly than that for acetone. In addition, the cost of propylene relative to that for butenes is likely to increase, due to a developing shortage of propylene. Thus, a process that uses butenes instead of propylene as feed and coproduces methyl ethyl ketone rather than acetone may be an attractive alternative route to the production of phenol.
It is known that phenol and methyl ethyl ketone can be produced by a variation of the Hock process in which sec-butylbenzene is oxidized to obtain sec-butylbenzene hydroperoxide and the peroxide decomposed to the desired phenol and methyl ethyl ketone. An overview of such a process is described in pages 113-421 and 261-263 of Process Economics Report no. 23B entitled “Phenol”, published by the Stanford Research Institute in December 1977.
In addition, U.S. Pat. No. 5,298,667 discloses a process for producing phenol and methyl ethyl ketone which comprises the steps of oxidizing sec-butylbenzene to obtain a reaction liquid containing sec-butylbenzene hydroperoxide as the main product, concentrating the reaction liquid by means of a distillation column to obtain a bottom liquid containing sec-butylbenzene hydroperoxide as the main component from the column bottom and decomposing the bottom liquid to obtain phenol and methyl ethyl ketone. The process requires that the sec-butylbenzene starting material is substantially free from (a) ethyl hydroperoxide, carboxylic acids and phenol, (b) styrenes or (c) methylbenzyl alcohol. However, the method used to obtain the required sec-butylbenzene is not disclosed.
European Published Application No. 1,088,809 discloses a process for producing phenol, methyl ethyl ketone and acetone by the oxidation of a mixture containing cumene and up to 25 wt % sec-butylbenzene and the subsequent Hock cleavage of the hydroperoxides, so that the ratio of the phenol:acetone:methyl ethyl ketone in the product can be controlled via the composition of the feed mixture. The feed mixture is produced directly by the alkylation of benzene with a corresponding mixture of propene and 1-butene/2-butene in the presence of a commercial alkylation catalyst such as AlCl3, H3PO4/SiO2 or a zeolite.
However, existing commercial catalysts for the alkylation of benzene with butenes, typically AlCl3 and solid phosphoric acid, produce not only sec-butylbenzene but also varying amounts of by-products, mainly isobutylbenzene, tert-butylbenzene, dibutylbenzenes and tributylbenzenes. Of these compounds, dibutylbenzenes and tributylbenzenes are readily separated from the reaction mixture and can then transalkylated to produce additional sec-butylbenzene. However, the boiling points of isobutylbenzene, sec-butylbenzene and tert-butylbenzene are 172.8° C., 173.5° C. and 169° C., respectively, and hence it is difficult to separate these compounds from each other by distillation. Moreover, isobutylbenzene and tert-butylbenzene are known to be inhibitors to the oxidation of sec-butylbenzene to the corresponding hydroperoxide. For example, the rate of oxidation of sec-butylbenzene, when the sec-butylbenzene contains 1% by weight of isobutylbenzene, decreases to about 91% of that when the sec-butylbenzene is free of isobutylbenzene. Similarly, when the isobutylbenzene content is 1.65% by weight, the rate of oxidation decreases to about 86%; when the isobutylbenzene content is 2% by weight, the rate of oxidation decreases to about 84%; and when the isobutylbenzene content is 3.5% by weight, the rate of oxidation decreases to as much as about 82%.
Therefore, in employing the Hock process to coproduce phenol and methyl ethyl ketone, it is important to minimize the amounts of isobutylbenzene and tert-butylbenzene formed as by-products during the alkylation step to produce the sec-butylbenzene.
U.S. Pat. No. 5,059,736 describes a process for producing sec-butylbenzene from benzene and n-butene, comprising reacting benzene and n-butene in the presence of a homogeneous liquid aluminum chloride complex catalyst, said catalyst comprising aluminum chloride, hydrogen chloride, and an aromatic hydrocarbon, wherein the amount of aluminum chloride used as a component of the complex catalyst is from 0.51 to 5% by weight of the benzene used, the reaction temperature is from 20° C. to 70° C., and the amount of isobutylbenzene formed as a by-product is such that the weight ratio of isobutylbenzene to sec-butylbenzene formed is not more than 0.01:1. However, as discussed above, even isobutylbenzene impurities of 1 wt % significantly inhibit the oxidation of sec-butylbenzene to the corresponding hydroperoxide.
It is known from, for example, U.S. Pat. No. 4,992,606 that the synthetic porous crystalline material known as MCM-22 is an effective catalyst for alkylation of aromatic compounds, such as benzene, with alkylating agents, such as olefins, having from 1 to 5 carbon atoms. Similar disclosures are contained in U.S. Pat. Nos. 5,371,310 and 5,557,024 but where the synthetic porous crystalline material is MCM-49 and MCM-56 respectively. However, there is no disclosure or suggestion in these references that MCM-22, MCM-49 or MCM-56 should be unusually selective to sec-butylbenzene when used to catalyze the alkylation of benzene with a C4 alkylating agent.
U.S. Pat. No. 4,891,458 discloses a process for the alkylation or transalkylation of an aromatic hydrocarbon, such as benzene, which comprises contacting the aromatic hydrocarbon with a C2 to C4 olefin alkylating agent or a polyalkyl aromatic hydrocarbon transalkylating agent, under at least partial liquid phase conditions, and in the presence of a catalyst comprising zeolite beta. Suitable olefin alkylating agents are said to include ethylene, propylene, butene-1, trans-butene-2 and cis-butene-2, or mixtures thereof, although the preferred olefins are ethylene and propylene. In the case of the reaction of benzene with n-butenes or polybutylbenzenes, the reaction product is said to include sec-butylbenzene but there is no disclosure as to the level of isobutyl benzene or tert-butyl benzene impurities.
According to the present invention, it has been found that the use of zeolite beta or an MCM-22 family zeolite as the catalyst in the alkylation of benzene with linear butenes produces sec-butylbenzene that is substantially free of isobutylbenzene and tert-butylbenzene and hence is an attractive feed for the Hock cleavage to produce phenol and methyl ethyl ketone.